We are better defining the natural history of Ataxia-Telangiectasia (A-T). 1) We have developed a clinical scoring system and applied that system to a cross-sectional cohort of AT patients. Among patients less than 18 years of age there is a clar correlation between age and cumulative AT score. 2) We have noted that there is length delay between average age at which neurologic systoms appear and average age of diagnosis. We have analyzed the reasons for the delay and its consequences. 3) We are surveying all patients for the presence of opportunistic infections and complications of immunization. 4) We have noted significant nutritional deficiencies in a sub-group of patients and are looking for correlations with neurologic dysfunction. 5) We have noted little or no correlation between severity of pulmonary disease and presence of immunodeficiency. Instead, there appears to be correlation between pulmonary disease and problems with swallowing.